Moment monitoring system for boom-cable type cranes

ABSTRACT

Cranes, forklift trucks, and other burden manipulation apparatus generally comprise an elongate boom or other burden member of controllably variable moment with respect to the normally stably supported weighty base member of the apparatus. The present invention discloses a moment monitoring system so as to caution or apprise the apparatus operator that the burden member moment has attained an arbitrarily prescribed subcritical-level which is somewhat below the moment critical-level (i.e., the burden moment at which the base member and the entire apparatus is rendered unstable and inoperative). The moment monitoring system generally comprises sensing means of the variable liquid pressure type to sense when the controllably variable burden has attained the selected subcritical-level, said sensing means actuatably extending from the apparatus burden member to the base member thereof and being connected through a hydraulic-electrical transducer to caution the apparatus operator of said subcriticallevel and allow him to take moment-reducing corrective action. If the operator fails to take corrective action at the moment subcritical-level, the apparatus burden manipulation power can be made to automatically shut-off at the burden moment proxcriticallevel, thus averting disaster.

United States Patent 1 Becker et a1.

[ MOMENT MONITORING SYSTEM FOR BOOM-CABLE TYPE CRANES [76] Inventors:James M. Becker, 5112 North 78th 3762 Ernst St., both of Omaha. Nebr.68112 [22] Filed: June 5, 1972 [21] Appl. No.: 259,565

[52] 0.8. CI. 212/39 R, 340/267 C [51] Int. Cl. 1366c 13/48 [58] Fieldof Search 212/39 R, 39 I, 39 MS; 340/267 C [56] References Cited UNITEDSTATES PATENTS 3,641,551 2/1972 Sterner 212/39 3,638,211 1/1972 Sanchez212/39 MS FOREIGN PATENTS OR APPLICATIONS 1,155,192 6/1969 Great Britain212/39 R 1,255,263 11/1967 Germany 212/39 Primary Examiner-Even C. BlunkAssistant ExaminerH. S. Lane Attorney-George R. Nimmer [57] ABSTRACTCranes, forklift trucks, and other burden manipulation Nov. 13, 1973apparatus generally comprise an elongate boom or other burden member ofcontrollably variable moment with respect to the normally stablysupported weighty base member of the apparatus. The present inventiondiscloses a moment monitoring system so as to caution I or apprise theapparatus operator that the burden member moment has attained anarbitrarily prescribed subcritical-level which is somewhat below themoment critical-level (i.e., the burden moment at which the base memberand the entire apparatus is rendered unstable and inoperative). Themoment monitoring system generally comprises sensing means of thevariable liquid pressure type to sense when the controllably variableburden has attained the selected subcriticallevel, said sensing meansactuatably extending from the apparatus burden member to the base memberthereof and being connected through a hydraulicelectrical transducer tocaution the apparatus operator of said subcritical-level and allow himto take moment-reducing corrective action. If the operator fails to takecorrective action at the moment subcriticallevel, the apparatus burdenmanipulation power can be made to automatically shut-off at the burdenmoment proxcritical-level, thus averting disaster.

PAIENIEnuuv 1 3 191a 377L667 sum 2 or a MOMENT MONITORING SYSTEM FORBOOM-CABLE TYPE CRANES Cranes, forklift trucks, tuggers," fire-laddertrucks, elongate boom service vehicles, etc., are sometimes generallyreferred to as normally stable burden manipulation apparatus of thecontrollably variable moment type." For such class of apparatus, thereis a weighty base member normally stably supported upon the earth orother suitable underlying substrate whereby at apparatus stableconditions the base member extends vertically along an upright-axis andthe apparatus center-of-gravity is encompassed within the base member.Such apparatus class further comprises a burden member laterally offsetfrom the base member upright-axis and supported by the underlyingsubstrate throughJthe base member. If the operator allows the burdenmoment to become too great with respect to the base member upright-axis,the apparatus centerof-gravity will be shifted too far laterally; thebase member and the entire apparatus willno longer be stably supportedupon the underlying substrate, but rather might topple-over or otherwisebe rendered inoperative. Sometimes the burden member moment isdetermined by constant lateral distance and variable load, asexemplified by tuggers. Or, the burden member moment can be determinedby constant load and variable lateral distance from the base, memberupright-axis, such as in the case of tire-trucks with extensible obliqueladders. And, for analagous situations to forklift trucks and cranes,the burden member moment is determined by variable load and variabledistance from the base upright-axis. In any of the said threesub-classes of controllably variable burden moment apparatus, theoperator must be very attentive to the manner in which he controlls thepowered burden manipulation least its moment becomes so great as torenderthe apparatus unstable and inoperative. For example, there aremany recorded histories of operating cranes and forklift trucks wherethe burden moment with respect to the upright-axis had reached thecritical-level and the apparatus toppled thereby injuring the apparatusoperator. Attainment of the moment critical-level happens not only tounskilled and inattentive operators, but can also be caused bynon-operator factors such as mislabeled loads, mis-functioning lateraldistance controls, uneven substrates, etc.

It is accordingly the general object of the present invention to providea moment monitoring or surveilance system for cranes, forklift trucks,and other kinds burden manipulation apparatus, the system cautioning orotherwise apprising the apparatus operator that the It is another objectto provide moment monitoring systems for burden manipulation apparatusof various burden manipulation means, such as through driven cables,hydraulic power, etc. Exemplifying this object are hydraulic or cabletypes crans of various sophistication, hydraulic or cable typeforklifts.

It is yet another object to provide moment monitoring systems admirablyadapted for cranes of various design and sophistication, as well as forother burden manipulation apparatus.

With the above and other objects and advantages in view, which willbecome more apparent as this. description proceeds, the momentmonitoring system for burden manipulation type apparatuses generallycomprises sensing means of the variable liquid pressure type to sensewhen the controllably variable moment burden has attained an arbitrarilyprescribed subcritical-level,

7 said variable liquid pressure sensingmeans actuatably burden memberhas attained an arbitrarily prescribed subcritical-level which is nearto, but safely less then, the critical-level moment which would renderthe apparatus unstable.

It is a specific object to provide a moment monitoring system forvarious kinds of burden manipulation apparatus wherein the systemprovides an audible or visual warning to the operator whenever theburden moment has attained a selected subcritical-level. It is anancillary object to provide moment monitoring systems wherein, if theoperator fails to heed or to take moment-reduction corrective action atthe subcriticallevel, the system at a proxcritical-level automaticallyshuts-off the power to the apparatus burden manipulation.

extending from the apparatus burden member to the base member thereof,said liquid pressure sensing means being connected through ahydraulic-electrical transducer to apprise the apparatus operator thatthe prescribed subcritical-level of burden moment has been attainedwhereby he might take corrective action to decrease the burden momentand prevent the base member and the entire apparatus from being renderedunstable and inoperative.

In the drawing, wherein like characters refer to like parts in theseveral views, and in which:

FIG. 1 is a side elevational view of a typical burden manipulationapparatus with which the moment monitoring or surveilance system of thepresent invention might be employed, herein a crane wherein the elongatepivotal boom is angularly controlled with a hy draulic cylinder.

FIG. 1A is a simplified circuit diagram schematically indicating forFIG. 1 primary functions of the monitoring system hydraulicelectricaltransducer.

FIG. 2 is a top plan view of a respresentative form of ahydraulic-electrical transducer which might be utilized for the burdenmoment monitoring systems, including the systems of FIGS. 1 and 5.

FIG. 3 is a sectional elevational view taken along line 3-3 of FIG. 2.

FIG. 4 is a sectional elevational view taken along line 4-4 of FIG. 2.

FIG. 5 is a side elevational view of another kind of typical burdenmanipulation apparatus with which the moment monitoring systems of thepresent invention might be employed, herein a crane wherein the elongatepivotal boom is angularly controlled with a drumwound cable.

FIG. 5A is a simplified circuit diagram similar to FIG. 1A schematicallyindicating for FIG. 5 primary functions of the monitoring systemhydraulic-electrical transducer.

FIG. 6 is a circuit diagram similar to FIG. 1A, but wherein a typicalcrane is provided with outrigger stabilizers for the apparatus basemember.

FIG. 1 illustrates. atypical apparatus of the burden manipulationclasswith which the moment monitoring system concept of the present inventionmight be employed. Such typical apparatus (eLg. as crane 10), comprisesa weighty base member (herein generally referred to'as 10B) normallystably supported upon a suitable underlying substrate (e.g., earthssurface G) whereby at apparatus stable conditions the base membetextends vertically along an upright-axis (14V). The selected typicalapparatus further comprises a burden member (herein generally referredto M) laterally offset from the base member upright-axis and supportedby the underlying substrate wholly through the base member. Burdenmember 10M comprises an elongate boom 30 having its butt end 311pivotably attached at ml to the base member carriage portion and furthercomprises a load (as weights W) depending from the boom tip 33 wherebysaid burden member exhibits a moment, horizontally distance measuredfrom the base member upright-axis (14V), and dependent upon thecombination of load W plus the weight of boom 30. Thus, as boom 30pivots about 19F and its tip portion circumscribes arcuate locus 35, theburden moment is adapted to increase and even to the critical-levelextent where the base member is rendered unstable with respect to itssubstrate (G) thereby rendering the apparatus inoperative or eventoppled. The moment monitoring system of the present invention isintended to caution the apparatus operator whenever the moment attainsan arbitrarily prescribed subcritical-level, as by first warning him and(if necessary) by a subsequent automatic shutof for the apparatus burdenmanipulation power. The monitoring system generally comprises sensingmeans of the variable liquid type and extending from the apparatusburden member to the base member so as to sense when the burden momenthas attained an arbitrarily prescribed subcritical-level, and alsocomprises a hydraulic-electrical transducer actuatably connected to thesensing means to caution the apparatus operator that the prescribedsubcritical-level has been attained.

FIGS. 2-4 illustrate a representative form of a hydraulic-electricaltransducer, sometimes hereinafter referred to generally as transducer orT, which is adapted to convert the delta-pressure sensing means into theoperator cautioning means. Transducer T comprises a housing hereinhaving six rectangular panels, including four upright panels, ahorizontal floor-panel 81, and a horizontal removable roof-panel 82.Among the four upright panels is included a left-panel 83, a

right-panel 84, a rear-panel 85, and a front panel 86.

Positioned between panels 83 and 84 is a pressurespring 90 of theBourdon-Tube type and including a generally horizontal leading portion91 intersecting front-panel 86 (and secured thereat with collar 87),said pressure-spring extending rearwardly therefrom parallel to housingfloor-panel 81 toward rear-panel 85. Pressure-spring 90 also includes agenerally C-shaped portion 92 having a progressively decreasing tubulardiameter terminating at the pressure-spring narrowed trailing-end 93, ahorizontal bar 94 being rigidly attached to trail-end 93. Thus, as thevariable liquid pressure sensing means is introduced into the tubularpressure-spring 90 through its larger diameter leading portion 91, (asindicated at connections 45 and 64) progressively higher liquidpressures will cause the trailingend 93 and bar 94 to elevateprogressively higher above floor-panel 81 and bar 94 remains parallel to81. As will be pointed out, progressively higher elevations for thepressure-spring trailing-end 93 is sensed electrically throughrelatively movable contacts so as to caution the apparatus operatorrelative to the burden moment.

While the transducer T might provide onlyone signal to the operator, twosignal stages at two liquid pressure levels are preferred. For example,the hydraulicelectrical transducer T might include two horizontalelectrically conductive contact-plates K and L passing through andmaintained at constant elevation by housing front-panel 86. Althoughconstant elevation contact-plates K and L are physically located onopposite sides of pressure-spring whereby screw 95 overliescontact-plate K and screw 97 overlies contact-plate L. The lower end ofscrew 95 carries an electricalinsulator 88 to which is attached anelectrically conductive tall disc 96; an electrical conductor wire .I isre volvably or flexibly attached to disc 96 and proceeds therefromthrough housing front-panel 86. Similarly, the lower end of screw 97carries an electrically insulative member 89 to which is attached anelectrically conductive short disc 98; an electrical conductor wire N isrevolvably or flexibly attached to disc 98 and proceeds therefromthrough the housing front-panel 86. Thus, by virtue of the independentlyadjustable screws 95 and 97, the elevation of the respectiveelectrically conductive discs 96 and 98'with respect to bar 94 can beindependently established and the transducer calibrated thereby. Forexample, the elevation between disc 98 and contact-plate L can beestablished to be such that: for any liquid pressure change ofpressurespring 90 and a desired finite elevation increase of bar 94above co-elevation contact-plates K and L, conductor wire N willinitiate a warning to the apparatus operator at a subcritical-levelmoment before conductor wire J will shut-off or disable the momentcontrol power at a proxcritical-level. As will be pointed out later, thetransducer T will need to be calibrated for each apparatus classdepending upon stability characteristics of its base member and theburden member moment range.

Returning to the apparatus of FIG. 1 for a more detailed descriptionthereof, crane 10 is of the hydraulically actuated type which means thata hydraulic pump 43 provides the powering means for varying the burdenmoment. The base member 10B for crane apparatus 10 comprises a flat bedtruck 11 including cab 13 and a horizontally extending frame 12 havingdepending wheels whereby the weighty base member is stably supportedupon the earth G underlying substrate. Base member 108 further comprisesa carriage 15 revolvably supported at 14 upon frame 11 and revolvableabout upright-axis 14V, carriage 15 being provided with an operatorsseat accessible to operator controls (39, 49). There is a powerablyrevolvable drum 38 (controlled at 39) for winding load-cable 37 whichpasses from drum 38 to pulleys 35 and 36 at boom tip portion 33, theload W being attached to load-cable 37. Boom 30 has a controllablyvariable angle with respect to upright-axis 14V, as through hydrauliccylinder 40 having its casing pivotably attached at 41 to base memberframe 11 and its piston pivotably attached at 42 to the boom medialportion 32. The burden member (boom 30 and load W) has a variable momentwith respect to the base member upright-axis 14V as the boom angle ismade to increase with respect to 14V. Herein the burden member momentvariation powering means is the hydraulic pump 43 (controlled byoperator lever 49) which is motivated by the base member powerplant(e.g., ignition coil 47). Oil liquid is forced from pump 43 along hose44 to determine the length of cylinder 40 thereby determining theangularity of pivotal boom 30.

It can be readily appreciated that as the boom 30 angle with respect toupright-axis 14V increases, the increasing moment is exhibited or sensedas increasingly higher liquid pressures in cylinder 40 and in hose 44.For the purposes of the burden moment monitoring system of the presentinvention, a hose line 45 is employed to communicate with hose line 44and extends to the pressure-spring leading portion 91 of transducer T1,shown mounted to base member carriage 15. Thus, as the boom 30 angle toupright-axis 14V increases, the increasing burden moment will cause thepressurespring trailing-end 93 (and attached bar 94) to increase inelevation as indicated in phantom line in FIGS. 3 and 4, therebyelevating movable-contacts 96 and 98. Calibration of transducer T for aburden manipulation apparatus having a critical-level moment of someknown foot-pounds value Y might be as follows. First, there isarbitrarily selected some subscritical-valuelevel less than Y (e.g.,0.90Y foot-pounds), Which needs to be mathematically correlated in Zpounds per square inch through the variable liquid pressure sensingmeans, e.g., cylinder 40, slide pump 60, etc. Testing equipment (notshown) comprising a liquid reservoir, a pump, and a pressure gauge, isremovably attached to the pressure-spring leading portion 91 of thetransducer T and the liquid pressure is built-up to the Zp.s.i.(correlating to the selected subcriticablevel). At the maintainedZ p.s.i. level, one or both of the trans-. ducer screws (95,97) isappropriately adjustably calibrated. For example, at Z psi short disc 98should be arriving at contact-plate L while the lower end of tall disc96 is at contact-plate K. Then, at the correlated Z- plus psi. for theproxcritical-level, the lower end of disc 96 should be abovecontact-plate K. A bell, horn, light, or other warning device 48 isattached to base member and electrically connected with wire N to disc98. An electrical voltage (e.g., battery 46) is attached to base member15 and electrically connected with wire J to both contact-plate K andL(e.g., through connector-strip KL). The burden moment manipulationpowering means (e.g., ignition coil 47 is attached with wire J to disc96. Thus, if the operator of crane 10 should allow the moment of burdenmember IBM to reach the subcritical-level, the operator would becautioned by the warning device 48. If the operator fails to heed thewarning a'ndthe burden moment attains the proxcritical-level, the burdenmanipulation powering means (e.g., pump 43 through coil 47) isautomatically shutoff. Then, the operator would need to intervene anddrop the load (load-cable 37 and W) to G so that the delta-pressuresensing means (e.g., 40,60) becomes reduced and the burden poweringmeans through 47 is re-startable under lower and safer burden momentconditions.

Turning now to FIG. 5, the crane apparatus shown is of the boom .-cabletype which means that a boom-cable 67 windable about a drum 68 providesthe powering means for varying the burden moment. In particular, thedrum 68 is powerably revolvable through the base member power-plant(e.g., including ignition coil 47), the operator being able to controlthe degree of drum rotation through control lever 69. Boom-cable 67extends from drum 68 to carriage pulley 18, thence to a pulley 34Acarried by the lug 34 of boom tip portion 33, and finally the boom-cabledead end is attached to the base member carriage 15 e.g., at lug 17. Itcan be readily appreciated that as the boom 30 angle with respect toupright-axis 14V increases, the increasing moment is manifested asincreasing tension upon boom-cable 67. For the purposes of the momentmonitoring system of the present invention, a conventionalreciprocatable or slide pump 60 having oil or other flowable liquidtherein is interposed as a link for the boom-cable; thus, increases inthe burden moment and the boom-cable tension will be exhibited or sensedas increasingly higher liquid pressures in pump 60 and in hose 64.Reciprocatable pump 60 substantially comprises an outer casing 61(herein attached to carriage lug 17) and further comprises a pistonportion 62, the narrowed axial shaft of which remote of casing 61 beingattached to boom-cable 67.

Hose 64 passes through the pump casing 61 and proceeds therefrom to thepressure-spring leading portion 91 of transducer T4, which isstructurally identical to T1 and mounted to base member 15. Thus, as theboom 30 angle to upright-axis 14V increases, the increasing burdenmoment will cause the pressure-spring trailingend 93 (and attached bar94) to increase in elevation thereby elevating movable-contacts 96 and98. Accordingly, if the operator through lever 69 were to allow theburden member moment to reach the subcritical-level, the operator wouldbe cautioned by a warning device 48. If the operator fails to heed thewarning, and the burden moment attains a proxcriticallevel, the burdenmanipulation powering means (e.g., drum 68 through coil 47) isautomatically shutoff. Then, the operator would need to intervene andrelease the drum 68 and drop the load (load-cable 37 and W) to substrateG so that the delta-pressure sensing means 60 indicates a very lowvalue. Thus, the transducer T allows the power-plant (e.g., coil 47) tobe re-started and the operator through lever 69 and drum 68 to abruptlydecrease the burden moment. If pump 60 were to leak so as to besubstantially devoid of fluid liquid therein, the moment monitoringsystem would not operate. Hence, there is a liquid pressure indicator,such as pressure-gauge 63, for slide pump 66). To re lieve the operatorfrom surveiling pressure-gauge 63, there can be electrical switches onpump 60 to indicate an absence of liquid therein (i.e., piston 62becomes freely extended from casing 61). in this vein, the electricalcircuitry for ignition coil 47 might pass through the proposedelectrical switches on pump 60 to disable the burden manipulation powerwhenever the liquid has been accidentally drained from pump 60.

Oftentimes cranes and other burden manipulation apparatus are providedwith Outriggers which are controllably downwardly extendable from thebase member to firmly abut the underlying substrate. Thus, the use ofOutriggers will effectively lower the base member center-of-gravitywhereby the burden moment critical-lever is higher. Accordingly, thearbitrarily prescribed subcritical-level and the proxcritical-level canbe greater. in this vein, a higher liquid pressure for the monitoringsystem sensing means is needed to actuate the warning 48 wheneverOutriggers are engaged; on the other hand, a lower liquid pressureactuates warning 48 whenever Outriggers are up(i.e., not in use).

' For example, in the typical crane apparatus situation,

and arbitrarily shown in FIG. 1, outrigger 50 is of the hydraulicallyactuatable type including a casing 51 pivotably attached to the basemember frame 11 and an extendable piston portion having a head-end 52adapted to'abut against substrate G. Pump 53 forces liquid along hose 54to actuate outrigger St), the base member power-plant (e.g., throughcoil 47) powering pump 53. A hose 55 extends from hose 54 to thepressure-spring leading portion 91 of transducer T2 (structurally likeT1, T3, T4) which is attached to base member carriage l5. A hose 56proceeds from hose 45 to the pressure-spring leading portion 91 oftransducer T3 which is also attached to carriage 15. As seen in FIG. 6,whenever the outrigger is not in use (i.e., up and not engaged withsubstrate G) the resultant relatively low pressure in hose 55 andconnected to transducer T2 keeps outrigger-light 58 on, reminding theoperator of the outriggers up condition. Transducer T3 is calibrated sothat relatively low liquid pressures (from hose 56) will make T3 respondelectrically as compared to transducer T4 (supplied with delta-liquidpressure from hose 45).

From the foregoing, the construction and operation of the momentmonitoring systems will be readily understood and further explanation isbelieved to be unnecessary. However, since numerous modifications andchanges will readily occur to those skilled in the art, it is notdesired to limit the invention to the exact construction shown anddescribed, and accordingly, all suitable modifications and equivalentsmay be resorted to, falling within the scope of the apended claims.

I claim:

1. In a boom-cable type crane burden manipulation apparatus comprising aweighty base member normally stably supported upon a suitable underlyingsubstrate whereby at apparatus stable conditions the base member extendsvertically along an upright-axis, said crane further comprising anelongate boom burden member having a tip end located remotely laterallyoffset from the apparatus base member upright axis and also having abutt end pivotably attached to said base member whereby the elongateboom is supported by the underlying substrate through the weighty basemember, said crane apparatus boom-cable being controllably windableabout a powerably revolvable drum located at the base member andproceeding from said drum to the boom tip end and thence ultimatelyconnected at the boom-cable dead end to said base-member, said craneapparatus base member also including drum powering means and ancillaryoperator controls for said revolvable drum thereby permitting selectableburden moment changes with respect to the stable base memberupright-axis and upon reaching a critical-level the burden moment willrender the base member unstable with respect to the underlying substrateand to the detriment of said cranes stability, the improvement of burdenmoment monitoring system and comprising:

A. Sensing means of the variable liquid pressure type and comprising areciprocatable pump interposed as a connector link between theboom-cable deadend and the apparatus base member and located in thevicinity of the boom butt end and said sensing means also comprising anelongate hose through which is urged increasing magnitudes of liquidpressure from said pump as the boom-cable at increasing burden momentconditions exerts' increasing tension upon said pump connector link; and

B. At least one transducer of the hydraulic-electrical type actuatablyconnected to a stationary hose portion of said variable liquid pressuresensing means, and a warning indicator electrically connected to thetransducer to caution the crane apparatus operator and personnel thatsome prescribed subcritical-level of liquid pressure from the hydraulicpump has been attained whereby the crane operator through said poweringmeans may take corrective action through said revolvable drum todecrease the burden moment and thereby prevent the base member and theentire crane apparatus from being rendered unstably supported on theunderlying substrate.

2. The burden moment monitoring system of claim 1 wherein the hydraulicpump is of the internal slidable type that is fully longitudinallyextended when there occurrs an absence of liquid therein, said hydraulicpump being also electrically connected through the transducer to thecrane drum powering means and to automatically shut-off same wheneverthe hydraulic pump is substantially devoid of liquid, and wherein theentire hose length from the hydraulic pump connector link to thehydraulic-electrical transducer remains stationary during hydraulicactuation of the transducer by the pump sensing means.

3. The moment monitoring system of claim 1 wherein the operatorcautioning means is adapted to occur in two distinct stages, the firststage being as a warning that the arbitrarily prescribed momentsubcritical-level has been attained, the second stage at an arbitrarilyprescribed proxcritical-level providing automatic shutoff to thepowering means for the burden moment variation and occurring if theoperator had failed to controllably decrease the burden moment throughthe powering means therefor, said arbitrarly prescribedproxcritical-level being of intermediate moment value to thesubcritical-level and the critical-level.

4. The moment monitoring system of claim 3 wherein thehydraulic-electrical transducer comprises a Bourdon-Tube typepressure-spring having a narrowed trailing-end adapted to changeelevation and in degree according to the liquid pressure introducedthereinto, the transducer also comprising for the electrical switchmeans two pair of electrical contacts and each pair including astationary-contact of constant elevation and a movable-contactco-movable with the pressure-spring trailing-end, one contacts pairbeing adjustably calibrated to ensure relative movement therebetweenwhenever the burden moment attains said subcriticallevel wherebyoperator warning occurs, the other contacts pair being independentlyadjustably calibrated to ensure relative movement therebetween as theburden moment attains said proxcritical-level whereby burdenmanipulation power shutoff occurs.

5. The moment monitoring system of claim ll wherein the crane basemember has optional outriggers firmly downwardly abuttable against theearths surface whereby the crane base member center-of-gravity islowered during use periods of said outriggers, said outriggers beingtied into the warning means so that when outriggers are down against thesubstrate a higher liquid pressure is required to actuate the warningmeans than when outriggers are up.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,771,667 Dated November l}, 1973 lnv fl James M. Becker et al.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

In the patent" heading, item should read as follows:

-- Inventorsi Jam M. Becker, 5112 North 78th St.

and William Jac'Lcso1 37o2Ernst St., both of Omaha, Nebr.----. Zip codes68131.; and 66112, respectively.

Signed and sealed this 30th day of April 197R.

(SEAL) Attest:

EDWARD MJ LETQHERJR. C. MARSHALL DANN Attesting; Officer Commissioner ofPatents 5 05M PO-1 05O (10-69) USCOMM-DC wan-P99 i U.S. GOVERNMENTPRINTING OFFICE 2 I989 O QGG'SQQ,

1. In a boom-cable type crane burden manipulation apparatus comprising aweighty base member normally stably supported upon a suitable underlyingsubstrate whereby at apparatus stable conditions the base member extendsvertically along an uprightaxis, said crane further comprising anelongate boom burden member having a tip end located remotely laterallyoffset from the apparatus base member upright axis and also having abutt end pivotably attached to said base member whereby the elongateboom is supported by the underlying substrate through the weighty basemember, said crane apparatus boom-cable being controllably windableabout a powerably revolvable drum located at the base member andproceeding from said drum to the boom tip end and thence ultimatelyconnected at the boom-cable dead end to said base-member, said craneapparatus base member also including drum powering means and ancillaryoperator controls for said revolvable drum thereby permitting selectableburden moment changes with respect to the stable base memberupright-axis and upon reaching a critical-level the burden moment willrender the base member unstable with respect to the underlying substrateand to the detriment of said crane''s stability, the improvement ofburden moment monitoring system and comprising: A. Sensing means of thevariable liquid pressure type and comprising a reciprocatable pumpinterposed as a connector link between the boom-cable dead-end and theapparatus base member and located in the vicinity of the boom butt endand said sensing means also comprising an elongate hose through which isurged increasing magnitudes of liquid pressure from said pump as theboom-cable at increasing burden moment conditions exerts increasingtension upon said pump connector link; and B. At least one transducer ofthe hydraulic-electrical type actuatably connected to a stationary hoseportion of said variable liquid pressure sensing means, and a warningindicator electrically connected to the transducer to caution the craneapparatus operator and personnel that some prescribed subcritical-levelof liquid pressure from the hydraulic pump has been attained whereby thecrane operator through said powering means may take corrective actionthrough said revolvable drum to decrease the burden moment and therebyprevent the base member and the entire crane apparatus from beingrendered unstably supported on the underlying substrate.
 2. The burdenmoment monitoring system of claim 1 wherein the hydraulic pump is of theinternal slidable type that is fully longitudinally extended when thereoccurrs an absence of liquid therein, said hydraulic pump being alsoelectrically connected through the transducer to the crane drum poweringmeans and to automatically shut-off same whenever the hydraulic pump issubstantially devoid of liquid, and wherein the entire hose length fromthe hydraulic pump connector link to the hydraulic-electrical transducerremains stationary during hydraulic actuation of the transducer by thepump sensing means.
 3. The moment monitoring system of claim 1 whereinthe operator cautioning means is adapted to occur in two distinctstages, the first stage being as a warning that the arbitrarilyprescribed moment subcritical-level has been attained, the second stageat an arbitrarily prescribed proxcritical-level providing automaticshutoff to the powering means for the burden moment variation andoccurring if the operator had failed to controllably decrease the burdenmoment through the powering means therefor, said arbitrarly prescribedproxcritical-level being of intermediate moment value to thesubcritical-level and the critical-level.
 4. The moment monitoringsystem of claim 3 wherein the hydraulic-electrical transducer comprisesa Bourdon-Tube type pressure-spring having a narrowed trailing-endadapted to change elevation and in degree according to the liquidpressure introduced thereinto, the transducer also coMprising for theelectrical switch means two pair of electrical contacts and each pairincluding a stationary-contact of constant elevation and amovable-contact co-movable with the pressure-spring trailing-end, onecontacts pair being adjustably calibrated to ensure relative movementtherebetween whenever the burden moment attains said subcritical-levelwhereby operator warning occurs, the other contacts pair beingindependently adjustably calibrated to ensure relative movementtherebetween as the burden moment attains said proxcritical-levelwhereby burden manipulation power shutoff occurs.
 5. The momentmonitoring system of claim 1 wherein the crane base member has optionaloutriggers firmly downwardly abuttable against the earth''s surfacewhereby the crane base member center-of-gravity is lowered during useperiods of said outriggers, said outriggers being tied into the warningmeans so that when outriggers are down against the substrate a higherliquid pressure is required to actuate the warning means than whenoutriggers are up.